Problem 9 - Campbell Biology Concepts & Connections

Question

Crows break the shells of certain molluscs before eating them by dropping them onto rocks. Hypothesizing that crows drop the molluscs from a height that gives the most food for the least effort (optimal foraging), a researcher dropped shells from different heights and counted the drops it took to break them. $$\begin{array}{|c|c|c|}\hline \begin{array}{c}\text { Height of } \\\\\text { Drop (m) }\end{array} & \begin{array}{c}\text { Average Number } \\\\\text { of Drops Required to } \\\\\text { Break Shell }\end{array} & \begin{array}{c}\text { Total Flight Height } \\\\\text { (Number of Drops } \times \\\\\text { Height Per Drop) }\end{array} \\\\\hline 2 & 55 & 110 \\\\\hline 3 & 13 & 39 \\\\\hline 5 & 6 & 30 \\\\\hline 7 & 5 & 35 \\\\\hline 15 & 4 & 60 \\\\\hline\end{array}$$ a. The researcher measured the average drop height for crows and found that it was \(5.23 \mathrm{~m}\). Does this support the researcher's hypothesis? Explain. b. Describe an experiment to determine whether dropping molluscs from an optimal height is learned or innate.

Step-by-Step Solution

Answer

The measured drop height (5.23m) supports the hypothesis as it is close to 5m, the height with the minimum total flight height of 30m. An experiment contrasting groups with and without exposure to the behavior could determine if it is learned or innate.

Step 1: Understand the Hypothesis

The researcher hypothesizes that crows drop molluscs from a height that minimizes total effort, which is the 'optimal foraging' strategy. This means finding the height that requires the least total flight height.

Step 2: Analyze the Data

Review the given data table. Each row signifies a different height, the average number of drops required to break the shell, and the resultant total flight height.

Step 3: Identify the Optimal Height

Check the 'Total Flight Height' column for the minimum value. The smallest total flight height indicates the optimal height that requires the least effort.

Step 4: Evaluate the Given Data

From the data: For 2m, Total Flight Height = 110m For 3m, Total Flight Height = 39m For 5m, Total Flight Height = 30m For 7m, Total Flight Height = 35m For 15m, Total Flight Height = 60m The minimum value is 30m at a height of 5m.

Step 5: Compare with Average Drop Height

Compare the identified optimal height (5m) with the measured average drop height for crows (5.23m). Since 5m is close to 5.23m, it supports the hypothesis.

Step 6: Experiment Design to Test Learning vs Innate Behavior

A possible experiment could involve raising young crows in two different environments: one where they observe older crows dropping molluscs and another where they have no exposure to this behavior. If the crows in both environments learn to drop molluscs from the optimal height, it suggests innate behavior. If only the observed group learns the optimal height, it suggests the behavior is learned.

Key Concepts

Behavioral Ecology

Behavioral ecology examines how an animal's behavior contributes to its survival and reproduction. How crows drop molluscs from specific heights is a prime example of this field in action. Crows might be using optimal foraging strategies to maximize the energy gained from food while minimizing effort. The concept revolves around the use of minimal energy for maximum reward, and it is fascinating to see such intelligent behavior in birds. By studying behaviors like these, scientists can gain insight into how animals interact with their environment and use their resources effectively.

Experimental Design

Designing a proper experiment is crucial for testing hypotheses in behavioral ecology. The crow mollusc-dropping experiment is an excellent illustration. The researcher hypothesized that crows choose drop heights that minimize effort and maximize food intake. To test this, they dropped the molluscs from various heights and counted the number of drops required to break them. By doing so, they could pinpoint the height that required the least total flight height, thus confirming or disproving the hypothesis. Key factors in experimental design include:

• Control of variables: Ensure all other conditions are constant.
• Repeatability: Enough trials to get an accurate measure.
• Observation: Precise data collection on drops and height.

This structured approach helps achieve reliable and reproducible results.

Innate vs Learned Behavior

Understanding if behavior is innate (genetic) or learned (acquired) is vital in behavioral studies. The crow example provides an enlightening scenario. To determine if dropping molluscs from an optimal height is innate or learned, an experiment could manipulate environmental exposure. Raise two groups of young crows:

• Group 1: Exposed to older crows demonstrating the behavior.
• Group 2: Raised without exposure to this behavior.

Compare the performance of both groups. If both groups drop molluscs from optimal heights without prior exposure, the behavior is likely innate. If only the first group learns it, then the observed behavior is learned. This kind of study helps clarify whether behaviors are hardwired or shaped by experience.

Data Analysis

Analyzing data accurately is essential for drawing valid conclusions. In the crow experiment, the researcher analyzed the total flight height for different drop heights. The steps of data analysis include:

• Examine the data: Look at the averages and trends.
• Identify patterns: Find minimum values and compare them.
• Evaluate significance: Determine if observed differences support the hypothesis.

For the crows, analyzing the total flight height revealed that a height of 5 meters was optimal (total flight height of 30 meters). This close match to the average drop height of 5.23 meters supports the hypothesis. By rigorously examining data, researchers can validate their theories and make informed conclusions.